This invention relates to cursive script recognition and in particular to cursive handwriting recognition methods and apparatus, that is, recognition of characters and words formed by a continuous stroke, wherein information on stroke order is provided in connection with input of stroke position information.
The field of computer-aided cursive script recognition is of interest since many individuals do not have the skills to communicate through a keyboard and since many tasks would be greatly expedited by the use of direct input to a computer through a familiar writing instrument, such as a pen, pencil or stylus. Cursive handwriting recognition is particularly challenging because the ciphers are formed by continuous strokes and because handwriting differs widely among individuals.
The work of Dr. Shelja A. Guberman of the former Soviet Union, one of the coinventors, forms the basis of the present invention. In a paper published in the Russian language journal Avtomatika i Telemekhanika, by Shelya A. Guberman and V. V. Rozentsveig under the title "Algorithm for the Recognition of Handwritten Text," (No. 5, May, 1976, pp. 122-129, UDC 681.39.06) the developers describe the state of the known art of cursive handwriting recognition and propose that the dynamic parameters of pen trajectory be used in connection with the various recognition algorithms. Among the recognition algorithms were feature matching to identify strokes, recognition of the start and finish of a trajectory, and the subdivision of a trajectory into elements, or as termed hereinafter, metastrokes. The developers, however, limited their alphabet of metastrokes to just seven self-intersecting elements and three arc elements. Moreover, the work was silent about the possibility of confusion among elements in the recognition process and did not consider the use of dynamic programming techniques. As a consequence, further development has been warranted in order to improve reliability and utility of recognition.
Elements of a number of techniques similar to those used in connection with the present invention have been disclosed in the past. These references serve to illustrate the state of the art. Details of specific embodiments of the present invention which might use these prior art techniques are therefore not described in depth. The following references are nevertheless of interest in the field of cursive handwriting recognition.
Ehrich and Koehler, "Experiments in the Contextual Recognition of Cursive Script," IEEE Transactions on Computers, Vol. C-24, No. 2, Feb. 1975, pp. 182-194. This paper describes the use of segregation techniques between main bodies of letters and ascenders and descenders as part of a prerecognition scheme.
U.S. Pat. No. 3,996,557 to Donahey describes a similar technique to that of Ehrich et al.
U.S. Pat. No. 3,133,266 to Frischkopf describes normalization in the Y direction, use of dictionary matches for recognition and rating of likelihood of accuracy of recognition of individual words.
U.S. Pat. No. 3,969,698 to Bollinger et al. describes an apparatus for post processing of words which have been misrecognized by a character recognition machine, a speech analyzer, or a standard keyboard.
U.S. Pat. No. 4,610,025 to Blum et al. describes the isolation of ascenders and descenders as part of an early analytical step and the isolation of words for identification.
U.S. Pat. No. 4,731,857 to Tappert and U.S. Pat. No. 4,764,972 to Yoshida et al. both describe word isolation as part of the analysis process.
U.S. Pat. Nos. 4,933,977 and 4,987,603 to Ohnishi et al. describes the elimination of extraneous marks in an input pattern, as well as the concept of recognition of elements that are less than complete characters, including straight lines, arcs and loops.
U.S. Pat. Nos. 3,111,646 and 3,127,588 to Harmon describe systems using features extraction recognition techniques as well as stroke sequence information.
U.S. Pat. No. 4,754,489 to Bosker describes a system for recognizing letter groupings called digrams and trigrams.
U.S. Pat. No. 5,034,989 to Loh describes a method for identifying individual handwritten letters.
These prior art references provide a background context for developing an understanding of the present invention. The present invention builds on prior techniques, combines many techniques not heretofore combined, and introduces new techniques heretofore unknown in order to attain an enhanced level of recognition.